Blog post

The world's most cost-effective rats?

4 min read
28 Mar 2013

APOPO is a remarkable organization which trains rats to detect cases of Tuberculosis in Tanzania [1]. While not everyone will agree that the giant rats used by APOPO are cute, they definitely seem to be effective. Once trained, these little guys can screen around 40 samples of sputum for TB in under 7 minutes [2]. That's the same amount as a full day's work for a lab technician! So how do these rats perform so well? The key is a combination of specialized training and the rats' attuned sense of smell.

The training process begins at a young age, by socializing the rats with human activity, allowing them to be comfortable with a wide array of stimuli. Next, the researchers establish a 'clicking' sound as a conditional reinforcer associated with a food reward. This association mechanism is used in the later stages of the training, where the rat will be rewarded for pausing over the samples positive for TB. After the rat has learned to consistently detect the unique smell produced by the TB positive sputum, they move onto the final testing apparatuses, where they test 10 samples in quick succession.

This may seem all well and good you might say, but isn't it a bit too low-tech to be effective? Surely advanced lab equipment is a better solution for detection of TB than rats. Not so! In fact, these little guys are arguably superior to contemporary advanced medical technology, both in their cost and in their effectiveness. In several of the trials run by APOPO, the rats select samples that were not marked TB positive in the original lab test, but after checking again in the lab, in fact TB positive, but were simply missed in the first round of lab tests [3]. Indeed, tests performed by the rats were found to be more accurate than the standard practice of microscopy [4] [5]. So not only are the rats more accurate than standard lab work, they are also far more cost effective.

A TB detecting rat takes about 9 months to train, the total cost of which is around $2,000 USD [6]. Compare this to a fairly simple Gene Xpert, a device designed to detect the unique genetic information of the TB bacteria. These devices cost around $17,000 [7] and a further $15-20 per test for the lab workers in Tanzania [8]. The rats are not only faster than standard technological methods (can accomplish in 7 minutes what usually takes a researcher a day) they function at at least one eighth the cost. Since the rats work approximately 60 times faster than the average lab worker at detecting TB [9], they are approximately 480 times more effective than standard methods [10]!

The data seems to have surprising results - rats, not advanced medical technology, may be the way to go in identifying positive cases of TB. This may turn out to be a great opportunity to 'push the rope sideways' - to do a great amount of good by finding an intervention which is supported by evidence, but has been overlooked by other funders because it's such an outlandish way of helping people. We're currently in conversation with APOPO to learn more about their work, and will keep you updated!


[2] As cited in Apopo's information video:!

[3] Global Post Interview

[4] Weetjens Bart J, Mgode Georgies F, Machang'u Robert S, Kazwala Rudovic, Mfinanga Godfrey, Lwilla Fred, et al. African pouched rats for the detection of pulmonary tuberculosis in sputum samples. Int J Tuberc Lung Dis. 2009; 13:737-743.

[5] Amanda M Mahoney, Bart J Weetjens, Christophe Cox, Negussie Beyene, Georgies Mgode, Maureen Jubitana, Dian Kuipers, Rudovic Kazwala, Godfrey S Mfinanga, Amy Durgin, Alan Poling. Using giant African pouched rats to detect tuberculosis in human sputum samples: 2010 findings.

The Pan African Medical Journal. 2011;9:28

[6] Global Post Interview


[8] Global Post Interview

[9] Referring to the 40 samples in 7 minutes cited above: (480min[8 hour work day]/7min[per sample] = 60)

[10] 60[times more samples per hour] x 8[less expensive] = 480. The numbers in this, and the previous note should be taken with a giant-rat sized grain of salt, as they are built on many crude generalizations, including the notion that the rats could work 8 hours a day. While the '480' figure doesn't, by any means, explain the complexities on both sides of the equation, I think it's fine so long as we treat it as a rough first pass.